Coupling apparatus



May 21, 1929. L. L. JONES COUPLING APPARATUS July 19, 1926 Filed 9 2 zou Patented May 21, 1929.

UNITED STATES LESTER LJ ONES, OF ORAIDELL, NEW JERSEY.

COUPLING APPARATUS.

Application filed July 19,

This invention relates to a coupling apparatus or transformer system, and relates more particularly to a coupling apparatus especially designed for use with radio circuits such as cascaded radio amplifying systems.

As is well known, it is a desideratum in certain types of selective and sensitive radio receiving apparatus and in apparatus employable near transmitting stations to construct the inductance coils of the receiving apparatus so that they are uncoupled magnetically and electrostatically to other coils and apparatus in the receiving circuit or to the transmitting apparatus. Toaccomplish the magnetic uncoupling of the coils to other apparatus, various types of coil windings have hitherto been designed, such as double D windings, toroidwindings and binocular coils; and to accomplish theelectrostatic uncoupling of such coils to surrounding apparatus, it has been common to employ separate electrostatic shields. coil windings have, however, been found insufficient to produce the desired results on ac- I count of their relatively large external fields near the coil which produce considerable coupling to other parts and even between similar coils when placed at a moderate distance apart. To reduce the intermagnetic couplings between similar coils in a radio receiving set with the use of such prior structures, it has been found necessary to so relatively arrange the coils one with respect to the other in the radio receiving set as to minimize the reacting fields. Other structural difficulties, such as the large volume of winding required and the difficulty of winding methods, have also hindered the use of these prior and known types of winding coils.

A prime desideratum of my present invention resides in the provision of a coupling apparatus or transformer embodying an inductance coil system designed and constructed so that the external magnetic field of the coil system is reduced to such a minimum. that the coil system is substantially decoupled magnetically from surrounding apparatus and may be placed in close proximity to other similar coil systems of a radio receiving set without intermagnetically reacting with the same. i e

A further prime desideratum of the invention resides in the provision of a'coupling apparatus or transformer embodying a coil system which is self-electrostatically shielded, that is, which requires no additional or These prior types of- 1926. 'Serial No. 123,347.

separate electrostatic shield structure, the

=coil system'being so designed and constructed that even when employed in a sharply tuned circuit'the'same will be so perfectly shielded electrostatically that the hand of the operator may be brought to touch and surround the coil structure without detuning the circuit.

It is a further object of the present invention to so design and construct the inductance coil system of the transformer that themathematical and empirical conditions which satisfy the relations to produce the magnetic shielding also satisfy the relations to produce the static shielding so that the coil system is' both electromagnetically and electrostatically decoupled from surrounding apparatus, permitting not only the close arrangement of'a plurality of transformers to produce a compactly organized radio receiving set, but permitting the same to be constructed without the use of the electrostatic shielding devices.

A further principal object of my present invention comprehends the provision of a variable coupling apparatus or variotransformer embodying the above-referred-to construction and one in which the coupling may be obtained over a very wide range, such for example over an inductance range of 50 to 1.

To the accomplishment of the foregoing and such other objects as will hereinafter appear, my invention consists in the elements and their relation one to the other as hereinafter more particularly described and sought to be defined in the claims; reference being had to the accompanying drawings which show the preferred embodimentof my invention", and in which:

The figure is a cross-sectional View of the coupling apparatus or transformer embody ing the principles of my inventionand showing the manner of connecting the same 1n c1rcuit.

the coupling apparatus of my presentinvention comprises a secondary generally designated as S embodying a coil system which is self-magnetically and electrostatically shielded and aprimary l? coupled thereto, the said primary being preferably variably coupled to produce a relatively large range of mutual in Referring now in detail to the drawings,

duct-an'ce change between the primary and secondary of the transformer.

The secondary coil system of my invention comprises an inner coil section A and an outer coil section B both preferably made in the form of solenoids arranged in coaxial relalie . tion, the inner coil section being wound on a drum 10 made of insulating material and the outer coil section being wound on a drum 11 made of insulating material, the said coil sections being related in the manner specified hereinafter so that the outer coil section B forms a magnetic and electrostatic shield for the inner coil section A.

The coil sections A and B are connected togather at contiguous ends by theconductor 12 so that the instantaneous currents traversing the coil sections are in opposite directions, or in other words, so that opposing fluxes of different magnitudes are produced in the core of the inner coil section A. Preferably shown the outer coil joins the inner coil at the same axial end so that the two coils may be wound in the same direction. The free end 13 of the inner coil section A is the high potential end and is connected to the hi h potential point of the radio receiving circuit, as shown in the drawings, and the free end 14 of ,the outer coil section is the ground end and is connectedin use to a point of ground potential in the radio receiving circuit. For reasons to be pointed out hereinafter, the outer coil preferably overlaps the inner coil and preferably so that the line joining their ends makes an angle of approximately 45 with the axis of the coils, as clearly shown in Fig. 1 oft-he drawings.

To produce the magnetic decoupling of the coil system, I have discovered thatthe ratio of the turns of the two coil sections must bear a definite and quite accurate relation to the ratio of the areas of the two coils. This relation is that the product of the area and the number of turns on one coilsection must be substantially equal to the product of the area and the numb-er of turns of the other coil section. The satisfaction of this condition reduces to a minimum the magnetic coupling between the coil system and a uniform magnetic field,

as well the magnetic coupling of the coil system with other similar coils. This will be bestunderstood when it is seen that if the coil system of my invention be placed in a uniform magnetic field of variable I intensity, which field is directed for point of illustration along the axes of the coils, the E. M. F. induced in the inner coil section is equal to the E. M. F. induced in the outer coil section, since the induced E. M. F. in a coil section is a linear function of the number of turns and the total flux threading the coil. Since the product of the area and number of turns for one coil is equal to the product of the number of turns and the area for the other coil, it follows that the induced E. M. F.s are equal. Conversely,

it will therefore be seen that the resultant tion. 'Ifthe field be not parallel to the axis.

as assumed, the same conditions exists, since inductance between thetwo coil sections A and B. When this condition is satisfied, there results the novel effectof no potential drop along the outer coil due to the high frequency currents flowing; so that the whole surface of the outer coil is at substantially one potential. if this potential be made the ground potential shown in the preferred use of the coil system, it will be seen that the coil system is substantially completely electrostatically shielded.

To make the self-inductance of the outer coil section B equal to the mutual inductance between tie coils, I have found first that the ratio of the turns of the two coils must bear the same relation to the ratio of the area of thotwo coils is necessary to satisfy the requirement of producing the magnetic shielding of the coil system hereinbefore dc scribed. Thus the product of the area and number of turns of one coil should be equal to the product of the area and the number of After satisfying this turns of the other coil. condition, whichis thesame for producing magnetic decoupling, it generally necessary only to make the length of the outer coil slightly greater than the length of the inner coil, as clearly shown in the drawings. This difference in coil length may be utilized as shown to improve the electrostatic shielding of the high potential end of the inner coil, or, wherethis is not of primary importance, the inner and outer coils may be related symmetrically with a little overhanging of the outer coil at each end. The latter slightly impairs the electrostatic shielding of the high potential end of the inner coil but slightly improves the magnetic shielding of the coil system.

vi henezract compliance with the last-unentioned condlion is effected, I have found hat it is possible to place ones hands about the outer coil without detuning, even though this coil be connected in a sharply tuned circuit shown in the drawings.

To produce a coil system of high efiiciency, I have found that the ratio of areas of the coil sections should bear a given relation. Generally the ratio of areas of the enter to the inner coil section may be between 5 to 1 a 1 ,4 to 1, and for producing the greatest eficiency the ratio of areas should be about 2, 2.1 and 2.2 for coils having ratios of 1.26, 1.58 and 2.1 respectively, of'outer coil diameter to length. These area ratios are considered desirable because they give a maximum inductance for a given length of coil system having a constant outside diameter when the inner coil is wound with a constant number of turns. This is a practical commercial limitation because other electrical and structural conditions impose certain limitations on coil diameters and coil lengths. The maximum number of turns perinch that can be wound on the solenoid form is usually determined by the wire diameter especially at short waves where multilayer or banked windings cause a large decrease in coil efliciency. \Vhere the area ratio. of outer coil to inner coil is about 2, I also obtain a high degree of static shielding with low distributed capacity in addition to obtaining maximum inductance with minimum resistance.

The results of magnetic and electrostatic shielding produced by my coil construction may also be visualized by consideration of the magnetic and electrostatic fields produced by the inter-acting coil sections. Magnetically considered, the magnetic flux through the inner coil due to the current in the inner coil, which flux is the more intense flux, is slightly reduced by the opposing flux through the inner coil due to the current in the outer coil. The inductance of the coil system arises primarily because the inner coil section has in its core a relatively intense magnetic field which is only partially neutralized bythe flux of the outer coil. This partially neutralized flux within the coil has for its return path the annular space between the coils. That portion of the flux of the inner coil which would. tend to return outside the outer coil is neutralized by the return flux of the outer coil. It follows, therefore, that the outer coil section confines the magnetic flux and is effective as a magnetic shield.

' Electrostatica-lly considered, we may first assume that we may neglect the potential drop along the outer coil section due to the resistance of the coil, since for the sharply tuned circuits in which these coils are to be used, the ratio of inductive to resistive drop is greater than 100 to 1. Now the inductive drop along the outer coil must be due to the magnetic flux linkages with this coil. Since practically the entire flux threading the coil system passes through the cone of the inner coil and back in the annular space between the coils, there is no resultant flux linkage with the outer coil. This statementis to be modified only with respect to the residual flux which I have found issues radially from the center of the coil system and tends to produce neutralizing flux linkages in the halves of the outer coil. Looking at the phenomenon from the viewpoint of self and mutual inductances, thev inductive drop along the outer coil due to its self-inductance is neutralized by the voltage drop due to the induced voltage arising from the mutual inductance of the. two coils, these being equalized. Similarly the voltage drop along'the inner coil is neutralized in part by the mutual between the coils, but the self-inductance of the inner coil being much greater than the self-inductance of the outer coil, the fraction of inductance ofthe inner coil lost due to the reverse mutual is inconsequential.

The prnnary co1l- P of the transformer comprises a relativelyshort'solenoid having a'diameter slightly less than thatof the inner coil section A of the secondary S, so that the same may be located within the coil section A of the secondary for coupling purposes. Preferably the primary P is located at the low potential end of the inner coil section A.

WVhenused in a radio frequency cascaded system, the said primary P is connected as shown to the plate circuit of an electron discoil section A by means which may comprise a supporting arm 15 pivotal about an-ai ris 0 so that the primary coil may swing through an arc XYZ. The coupling variation as the coil moves from the inner position OZ to the outer position OX is very rapid because of the astatic nature of the secondary combination. To secure the desired sufliciently tight coupling to the astatic systemfl'he clearances between the primary P and the lnner COll A of the secondary should be reduced to a minimum'. V

When the coupler is constructed in this ,manner I have found that it produces a very desirable relation between the motion of the primary coil and the change of coupling. This relation is an approximately logarithmic one whereby a given displacement produces approximately equal percentage changes of coupling at any position of the coupler between thelimits OXOZ shown. When used as a volume control in radio receivers this characteristic in the coupler produces easy and smooth control of volume for all stations both far and near.

Furthermore the coupling mechanism may be made compact and yet have a practically attainable very low minimum of coupling. l/Vhere one of the coils is astatic as shown it is notnecessary to separate the coils by distances large compared with the coil diametersin order to place one coil in a region or very weak field strength due to the other coil. Furthermore the full range of coupling variation may be effected with a relatively small movement of the movable element of the coupler.

For the preferred operation of the radio receiving system, it is highly desirable to arrange the parts so that the variation of coupling does not cause any substantial variation of tuning in the coil system, and to accomplish this the primary coil P should be close only to the ground end of the secondary so as to avoid building up capacitive shunts across the secondary coil system by reason of the capacity between the primary and secondary windings. The astatic nature of the secondary coils eliminates troublesome feed;- back couplings between a plurality of secondaries and the small size primary coil minimizes energy transfer to distant circuits by the magnetic fields due to currents flowing in the plate circuits.

The manner of designing and constructing the transformer of my present invention will in the main be fully apparent from the above detailed description thereof. The uses and the manifold advantages thereof, especially in radio frequency circuits of the tuned and selective types, will it is thought be also manifest from the above. While I have shown and described my invention in the preferred form, it will be obvious that many changes and modifications may be made in the structure disclosed Without departing from the spirit of the invention, defined in the following claims.

I claim:

1. A coupling apparatus comprising an astatic coil system including an inner coil section and an outer coil section connected to produce opposing fluxes of different magnitudes in the core of the inner coil section, the lroduct of the number of turns and area of the inner coil section being related to the product of the number of turns and area of the outer coil section to produce neutralizing magnetic fields at a distance, and a coil coupled to the astatic coil system, said coil beingmovable to and from a position within the inner coil section of the said astatic coil system.

2. A coupling apparatus comprising an astatic secondary including an inner inductance coil section and an outer shielding coil section connected so that the instantaneous currents traversing the same are in opposite directions, the product of the number of turns and area of the inner inductance coil section being equal to the product of the number of turns and area of the outer shielding coil section, and aprimary coupled to the astatic secondary, said primary being movable to and from. a position within the inner coil section of the said secondary.

3. A coupling apparatus comprising an astatic coil system. including. an inner coil section and an outer coil section connected so that the instantaneous currents traversing tion, and a coil coupled to the astatic coil system, said coil being movable to and from a position within the inner coil section of the said astatic coil system.

4. A coupling. apparatus comprising an astatic secondary including an inner coil section and an outer coil section connected to produce opposing fluxes of different magnitudes in the core of the inner coil section, the selfinductance of the outer coil section being equal to the mutual inductance between the coil sections, whereby the outer coil section forms a static shield for the coil system, and a primary coupled to the astatic secondary, said primary being movable from a position within and at the low potential end of the inner coil section to a position exterior thereto.

5. A coupling apparatus comprising an astatic secondary including an inner inductance coil section and an outer shielding coil section connected so that the instantaneous currents traversing the same are in opposite directions, the product of the number of turns and area of the inner inductance coil section being. equal to the product of the number of turns and area of the outer shielding coil section, and the length of the outer coil section being slightly greater than the length of the inner coil section whereby the outer coil section forms the static and mag netic shield for the coil system, and a pri mary coupled to the astatic secondary, said primary being movable from a position within and at the low potential end of the inner coil section to a positionv exterior thereto. 7

6. A coupling apparatus comprising an astatic coil system including an inner coil section and an outer coil section connected to produce opposing fluxes of different magnitudes in the core of the inner coil section, the product of the number of turns and area of the inner coil section being related to the product of the number of turns and area of the outer coil section to produce neutralizing magnetic fields at a distance, and a coil coupled to the astatic coil system, said coil being located within the inner coil section of the said astatic coil system.

7. A coupling apparatus comprising an astatic secondary including an inner coil sec tion and an outer coil section connected to produce opposing fluxes of different magnitudes in the core of the inner coil section, the outer coil section forming an electrostatic and electromagnetic shield for the secondary, and a primary coupled to the astatic secondary, said primary being located so as to be threaded by the flux flowing through the core of the inner coil section of the secondary.

8. A coupling apparatus comprising an astatic secondary including an inner inductance coil section and an outer shielding coil section connected so that the instantaneous currents traversing the same are in opposite directions, and a primary coupled to the astatic secondary, saidprimary being located so as to be threaded by the flux flowing through the core of the inner coil section of the secondary.

Signed at New York city, in the county of 5 

